Question 213832
s=1/3(pie)hr^2+4(pie)rh 
It's pi, the Greek letter, not pie, the dessert.
{{{s=(pi*hr^2)/3+4pi*rh }}}
{{{r^2*(h*pi/3) + r*4*pi*h - s = 0}}}
{{{r^2 + 12r - 3s/(pi*h) = 0}}}
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Use the quadratic formula
{{{r = -6 + sqrt(36 + 3s/(pi*h))}}}
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{{{r = -6 - sqrt(36 + 3s/(pi*h))}}} If s is >0 this will give a negative value for r, so ignore it.